Brake disc for railway vehicle

ABSTRACT

A brake disc for a railway vehicle includes: a disc plate portion that has a sliding portion of a front face; a plurality of radial fins that are provided on the rear face of a disc plate portion, and that have a shape that extends in the radial direction of the disc plate portion; and a circumferential rib that is provided between each pair of adjacent radial fins, and that has a shape that extends in the circumferential direction of the disc plate portion. A flow path for air is formed between the pair of radial fins, and the flow path for air is narrowed by the circumferential rib. On the circumferential rib, a gradual slope for suppressing fluctuations in an airflow that passes between the pair of radial fins is provided from a base part to a top part.

TECHNICAL FIELD

The present invention relates to a brake disc for a railway vehicle thatis fastened to a wheel of a railway vehicle and generates a brakingforce by means of a sliding-contact member being pushed against asliding portion.

BACKGROUND ART

There are brake systems already in use which, with a brake disc fastenedto a wheel of a railway vehicle, slows or stops rotation of the wheel bypushing a sliding-contact member against the brake disc. In such brakesystems, a large amount of frictional heat arises at the brake discduring braking. Therefore, in some cases a structure is adopted in whicha plurality of radial fins that extend in the radial direction areprovided on the rear face of the brake disc to thereby cause air to flowbetween the brake disc and the wheel by rotation of the brake disc andthereby release heat from the brake disc.

In the case of a brake disc that has a plurality of radial fins, whenthe brake disc is mounted in a rapid-transit railway vehicle and a wheelwith the brake disc rotates at a high speed, a large amount of air flowsbetween the brake disc and the wheel and generates a large noise.Therefore, Patent Literature 1 proposes to provide a circumferential ribthat imparts resistance to air flowing between a plurality of radialfins and adjust an opening area between the radial fins by means of thecircumferential rib, for suppressing the amount of air that flowsbetween the plurality of radial fins to thereby reduce noise.

CITATION LIST Patent Literature

Patent Literature 1: JP2007-205428A

SUMMARY OF INVENTION Technical Problem

By providing a circumferential rib in a brake disc that has a pluralityof radial fins as described in Patent Literature 1, noise can be reducedin comparison to a case where a brake disc has no circumferential rib.However, in the case of the brake disc described in Patent Literature 1,in order to reduce the noise that arises as the air flow rate increasesdue to an additional increase in speed, it is necessary to furtherreduce an opening area between the circumferential rib and the wheel.When the opening area is reduced in this way, the problem arises that,because of a reduction in the air flow rate, the heat-releaseperformance of the brake disc cannot be adequately secured.

The present inventors performed tests to ascertain the sound sources ofa brake disc for the purpose of developing a low-noise brake disc thatdoes not lower the heat-release performance of the brake disc.

First, the sound sources of a brake disc rotating at high speed as wellas sound sources around the brake disc were investigated using amicrophone array sound source location system. As a result, it wasrevealed that sound sources are present in the vicinity of the brakedisc and within the brake disc. Next, a test was performed in which eachportion of the brake disc that was thought to generate a turbulent flowthat became a noise source was blocked up. Specifically, the term “eachportion” refers to an inlet (opening portion on the innercircumferential side of the brake disc) and an outlet (opening portionon the outer circumferential side of the brake disc) of a flow path forair on the disk rear face, and an opening end on the disk front face(sliding portion) side of each through-hole through which a bolt forfastening the brake disc to a wheel is inserted. It was confirmed that,as the result of blocking up all of the aforementioned portions andperforming a noise test, the noise generated from the brake disc wasreduced to an extremely low level. Further, a test was performed inwhich one location among the aforementioned locations was not blockedup, and the remaining two locations were blocked up. As a result it wasconfirmed that noise of a specific frequency is generated at therespective portions.

However, it was found that even when all of the aforementioned noiseswere added together, the noise level was lower than at a normal time,that is, a state in which all the regions are open. In particular, therewas a large difference in a high frequency range of 800 Hz or more.

The present inventors analyzed the results of these tests, and reachedthe conclusion that noise caused by fluctuations in an airflow on thebrake disc rear face is the largest factor, and completed the presentinvention by performing tests in which the shape of a circumferentialrib that produces fluctuations in such an airflow was changed in variousways.

An objective of the present invention is, with respect to a brake discfor a railway vehicle, to significantly reduce noise that arises from abrake disc during high-speed rotation of a wheel, without lowering theheat-release performance of the brake disc.

Solution to Problem

The present invention is a brake disc for a railway vehicle thatincludes: a disc plate portion having a sliding portion on a front face(a plate-like portion excluding radial fins and a circumferential riband the like that are described below of the brake disc is referred toas a “disc plate portion”); a plurality of radial fins provided on arear face of the disc plate portion and having a shape extending in aradial direction of the disc plate portion; a circumferential ribprovided between each pair of radial fins that are adjacent among theplurality of radial fins, and having a shape extending in acircumferential direction of the disc plate portion; wherein: a flowpath for air that runs from an inner circumferential side to an outercircumferential side of the disc plate portion is formed between thepair of radial fins in a state in which the disc plate portion isfastened to a wheel of a railway vehicle, and the flow path for air isnarrowed by the circumferential rib; and a gradual slope for suppressingfluctuations in an airflow that passes between the pair of radial finsis provided on the circumferential rib on a side face along the radialdirection of the disc plate portion.

According to this configuration, an action whereby air passing between apair of radial fins is disturbed by a circumferential rib and generatesa large noise is suppressed, and by this means noise that is generatedfrom the brake disc during high-speed rotation can be reduced by a largemargin. Therefore, noise can be reduced by a large margin withoutreducing the area of an opening portion between the circumferential riband the wheel which influences the heat-release performance.

Preferably, the gradual slope may be provided on one side face of thecircumferential rib that faces the inner circumferential side along theradial direction of the disc plate portion, or on both side faces of thecircumferential rib that face the inner circumferential side and theouter circumferential side, respectively, along the radial direction ofthe disc plate portion.

According to this configuration, by at least one of the side faces ofthe circumferential rib being formed to have a gradual slope facingtoward the inner circumferential side along the radial direction of thedisc plate portion, noise that is generated by fluctuations in anairflow that passes the circumferential rib can be reduced.

More preferably, the gradual slope may have a configuration including atop-part gradual slope that is provided at least at a top part of thecircumferential rib,

-   -   wherein the top-part gradual slope is a convex curved face        having a radius of curvature of 2 mm or is a sloping face which        is more gradual than the convex curved face, the top-part        gradual slope being provided at a side portion facing the inner        circumferential side of the disc plate portion, at a section of        2 mm or more in the radial direction of the disc plate portion,        and at a section of 2 mm or more in a rotational axis direction        of the disc plate portion from a vertex of the circumferential        rib.

More preferably, the gradual slope may have a configuration having atop-part gradual slope that is provided at least at a top part of thecircumferential rib,

-   -   wherein the top-part gradual slope is a convex curved face        having a radius of curvature of 5 mm or is a sloping face which        is more gradual than the convex curved face, the top-part        gradual slope being provided at a side portion facing the inner        circumferential side of the disc plate portion, at a section of        5 mm or more in the radial direction of the disc plate portion,        and at a section of 5 mm or more in a rotational axis direction        of the disc plate portion from a vertex of the circumferential        rib.

According to these configurations, noise generated at thecircumferential rib can be reduced without increasing the volume of thecircumferential rib. When the brake disc undergoes thermal expansion andthermal contraction, and hence stress fluctuations arise in a bolt thatfastens the brake disc to the wheel and the volume of thecircumferential rib increases, the rigidity of the brake disc increases,and hence the stress range of the bolt increases. According to the aboveconfigurations, because the volume of the circumferential rib can bemade small, the stress range that arises in a bolt can be made smallwhile also reducing the noise.

Specifically, a configuration is adopted in which the circumferentialrib connects the pair of radial fins, and which has a flow path for airbetween the wheel and the circumferential rib.

In this configuration, the aforementioned effect of reducing noise thatis realized by the gradual slope is obtained to a further degree.

Advantageous Effects of Invention

According to the present invention, in a brake disc for a railwayvehicle, noise that arises from the brake disc during high-speedrotation of a wheel can be reduced by a large margin without loweringthe heat-release performance of the brake disc.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view illustrating one example of a brake systemin a railway vehicle.

FIG. 2 is a plan view illustrating the rear face of a brake disc of afirst embodiment.

FIG. 3A is a cross-sectional view along a line indicated by arrows A-Ain FIG. 2, that shows a cross-section of respective portions of thebrake disc.

FIG. 3B is a cross-sectional view along a line indicated by arrows B-Bin FIG. 2, that shows a cross-section of respective portions of thebrake disc.

FIG. 3C is a cross-sectional view along a line indicated by arrows B-Bin FIG. 2, that shows a cross-section of respective portions of thebrake disc, and which shows a modification of the circumferential rib.

FIG. 4A is a plan view of a front face side of the brake disc, thatillustrates a brake disc according to a second embodiment.

FIG. 4B is a cross-sectional view along a line indicated by arrows C-Cin FIG. 4A, that illustrates the brake disc according to the secondembodiment.

FIG. 5 is a graph showing test results with respect to noise relating toa radial fin and a circumferential rib.

FIG. 6 is a graph showing test results with respect to noise relating athrough-hole for a bolt.

FIG. 7 is a view for describing an average inclination angle of agradual slope.

FIG. 8 is a graph that illustrates the relation between the volume of acircumferential rib and a bolt stress range.

FIG. 9 is a chart for describing a first form L1 to a fifth form L5 ofthe circumferential rib and a comparative form L6 shown in FIG. 8.

FIG. 10 is a view for describing a circumferential rib of the thirdembodiment.

FIG. 11 is a frequency graph showing a comparison of noise levelsbetween circumferential ribs of the third embodiment and a conventionalcircumferential rib.

FIG. 12 is a chart that shows the forms of the circumferential ribs thatare compared in FIG. 11.

FIG. 13 is a graph which compares overall noise levels of prescribedfrequency ranges.

FIG. 14 is a multiple view drawing for describing the forms of groovesprovided in a front face of a disc plate portion, in which FIG. 14A toFIG. 14E show a first form to a fifth form, respectively.

FIG. 15 is a frequency graph illustrating the relation between the widthof grooves and the noise level.

FIG. 16 is a frequency graph illustrating the relation betweenconnection locations of grooves and the noise level.

FIG. 17 is a graph illustrating the relation between a connection formof a groove and the overall noise level of prescribed frequency ranges.

DESCRIPTION OF EMBODIMENTS

Hereunder, respective embodiments of the present invention are describedin detail referring to the accompanying drawings.

(First Embodiment)

FIG. 1 is a perspective view that illustrates one example of a brakesystem in a railway vehicle. FIG. 2 is a plan view that illustrates arear face of a brake disc of a first embodiment. FIG. 3 is a multipleview drawing illustrating cross-sections of respective portions of thebrake disc, in which FIG. 3A is a cross-sectional view along a lineindicated by arrows A-A in FIG. 2, FIG. 3B is a cross-sectional viewalong a line indicated by arrows B-B in FIG. 2, and FIG. 3C is across-sectional view along a line indicated by arrows B-B in FIG. 2,which shows a modification of a circumferential rib.

Hereunder, a side facing toward an outer circumference along a radialdirection of a brake disc 10 is defined as an “outer circumferentialside”, and a side facing toward an inner circumference along the radialdirection of the brake disc 10 is defined as an “inner circumferentialside”.

A brake system of the first embodiment of the present invention ismounted in a rapid-transit railway vehicle. The brake system includes:the brake disc 10 that is fastened to a side portion of a wheel 100 ofthe railway vehicle, a sliding-contact member 200 that contacts againstthe brake disc 10 to generate a braking force, and a movable portion 210that is capable of pressing the sliding-contact member 200 in adirection in which the sliding-contact member 200 contacts the brakedisc 10. Although the configuration is not particularly limited, thebrake disc 10 and the sliding-contact member 200 are each provided onboth side faces of each wheel 100, and the movable portion 210 isconfigured to sandwich the wheel 100 by means of two of thesliding-contact members 200.

The brake disc 10 is an annular disc, and a front face 10 f of a discplate portion is a sliding portion. A plurality of radial fins 11 a and11 b, and a plurality of circumferential ribs 13 are provided on a rearface 10 r of the disc plate portion. In the brake disc 10, a plate-likeportion that excludes the radial fins 11 a and 11 b and thecircumferential ribs 13 is called a “disc plate portion”.

Further, a plurality of through-holes 12 for passing bolts through fromthe front face to the rear face are provided in the brake disc 10. InFIG. 2, to avoid complication of the illustration, only some of theradial fins 11 a and 11 b, the through-holes 12, and the circumferentialribs 13 are denoted by reference characters.

The radial fins 11 a and 11 b are portions having a shape extending inthe radial direction of the disc plate portion which protrude from therear face of the disc plate portion toward a plate portion of the wheel100. The plurality of radial fins 11 a and 11 b are provided atapproximately even intervals in the circumferential direction of thedisc plate portion.

The circumferential rib 13 has a shape that extends in thecircumferential direction of the disc plate portion, and is providedbetween each pair of adjacent radial fins 11 a and 11 b among theplurality of radial fins 11 a and 11 b so as to connect the relevantpair of radial fins 11 a and 11 b.

The plurality of through-holes 12 are provided on the same diameter ofthe disc plate portion, and are aligned at even intervals in thecircumferential direction of the disc plate portion.

As illustrated in FIG. 3A, a top part of the radial fins 11 a and 11 bcontacts a side face of the wheel 100. The circumferential rib 13 has aheight such that a gap exists between the top part of thecircumferential rib 13 and the wheel 100. By means of thisconfiguration, when the brake disc 10 is fastened to the wheel 100, aflow path for air is formed that is surrounded by the radial fins 11 aand 11 b, the rear face 10 r of the disc plate portion, and the plateportion of the wheel 100. Further, when the wheel 100 and the brake disc10 rotate, air flows from the inner circumferential side to the outercircumferential side through the aforementioned flow path, and by thismeans heat of the brake disc 10 is released.

In the present embodiment a gradual slope is formed on a side face 13 aon the inner circumferential side and on a side face 13 b on the outercircumferential side of the circumferential rib 13. The inclinationangle of the gradual slope is smaller than the casting draft angle, andpreferably the gradual slope is formed with an average inclination angleof 50° or less, and more preferably with an average inclination angle of45° or less. The term “draft angle” means, when the brake disc 10 iscast, a gradient that is closest to 90° among gradients that enable thecircumferential rib 13 to be molded and extracted from the mold withoutperforming undercut processing. In FIG. 3B and FIG. 3C, the draft angleis indicated by an imaginary line. In the gradual slope of thecircumferential rib 13, the average inclination angle is less than theslope of the side faces of the radial fins 11 a and 11 b. Here, the term“average inclination angle” means, as illustrated in FIG. 7, an angle αformed by a straight line A-B linking an end point A of roundingprocessing on a base side on the side face 13 a of the circumferentialrib 13 and an end point B of rounding processing on a top side of theside face 13 a, and a straight line A-C that is parallel to the platesurface of the brake disc 10.

The side faces 13 a and 13 b having a gradual slope of thecircumferential rib 13 may be formed to have a curved surface shapehaving a bulge, or to have a curved surface shape having a hollow, or tohave a flat surface or circular conical surface shape.

The actions of the brake disc 10 of the first embodiment will bedescribed later.

(Second Embodiment)

FIG. 4 is a multiple view drawing illustrating a brake disc according toa second embodiment, in which FIG. 4A is a plan view of a front faceside (sliding portion side) of the brake disc, and FIG. 4B is across-sectional view along a line indicated by arrows C-C in FIG. 4A.

Similarly to the first embodiment, the brake system of the secondembodiment of the present invention is mounted in a rapid-transitrailway vehicle. In the brake system, a brake disc 10A is fastened to aside portion of the wheel 100 (FIG. 1) of the railway vehicle, and thesliding-contact member 200 (FIG. 1) is pushed against the front face ofthe brake disc 10A to generate a braking force.

A plurality of through-holes 12 that pass through from a front face 10 fto the rear face, and a groove 15 that links the plurality ofthrough-holes 12 on the front face 10 f are provided in the brake disc10A.

The plurality of through-holes 12 are provided on the same diameter ofthe brake disc 10A, and are provided at even intervals in thecircumferential direction of the brake disc 10A. As illustrated in FIG.4B, each through-hole 12 has a minor diameter portion 12 t with a smalldiameter which allows the shaft of a bolt to pass therethrough, and amajor diameter portion 12 w with a large diameter at which the head of abolt or a nut is to be disposed. The major diameter portion 12 w mayhave a depth such that the head of a bolt or a nut sinks therein, or mayhave a configuration in which the depth thereof is shorter than theheight of the head of a bolt or a nut, and a part of the head of a boltor a nut projects into the groove 15. Further, the depth of the majordiameter portion 12 w may be made the same as the height of the head ofa bolt or a nut. In each of these cases, the head of the bolt or the nutdoes not project further outward than the front face 10 f of the brakedisc 10.

The groove 15 is formed in an annular shape so as to link the pluralityof through-holes 12 in the front face part of the brake disc 10A. Thegroove 15 is provided, for example, such that the shape thereof is alonga concentric circle of the brake disc 10A.

The structure that links the plurality of through-holes 12 by means ofthe groove 15 may be adopted in the brake disc 10 having the radial fins11 a and 11 b and the circumferential ribs 13 of the first embodiment,or may be adopted in a brake disc having a different structure to thefirst embodiment.

<Actions and Effects>

FIG. 5 is a graph showing results of noise tests relating to radial finsand circumferential ribs. FIG. 6 is a graph showing results of noisetests relating to through-holes for bolts.

FIG. 5 and FIG. 6 show test results with respect to a conventional brakedisc. The term “conventional brake disc” means a brake disc which hasradial fins, circumferential ribs, and through-holes for bolt, in whichthe circumferential ribs are in the shape illustrated by a chaindouble-dashed line in FIG. 3B, and the groove 15 is not provided in thefront face part of the disc plate portion. In FIG. 5 and FIG. 6, a graphline E represents the noise level when the conventional brake disc isrotated at high speed together with a wheel. A graph line L representsthe noise level when the conventional brake disc is rotated at highspeed together with a wheel in a state in which only the through-holesfor bolts are blocked up. A graph line H in FIG. 5 represents the noiselevel when the conventional brake disc is rotated at high speed togetherwith a wheel in a state in which all portions are blocked up except foropening portions on the outer circumferential side of flow paths for airof pairs of adjacent radial fins. A graph line I in FIG. 5 representsthe noise level when the conventional brake disc is rotated at highspeed together with a wheel in a state in which all portions are blockedup except for opening portions on the inner circumferential side of theaforementioned flow paths for air. A graph line F in FIG. 6 representsthe noise level when the conventional brake disc is rotated at highspeed together with a wheel in a state in which the aforementionedopening portions on the inner circumferential side and outercircumferential side of the flow paths for air and the through-holes forbolts are blocked up. A graph line G in FIG. 6 represents the noiselevel when the conventional brake disc is rotated at high speed togetherwith a wheel in a state in which all portions are blocked up except forthe through-holes for bolts.

As a result of conducting the tests it was found that the noise of theconventional brake disc includes noise that arises which is attributableto the radial fins at opening portions on the outer circumferential sideor inner circumferential side of the aforementioned flow path for air,noise that arises which is attributable to the circumferential ribswithin the aforementioned flow path for air, and noise that arises dueto the through-holes for bolts.

The noise in a range W3 of the graph line I in FIG. 5 is estimated to benoise which is attributable to radial fins at opening portions on theinner circumferential side. Further, the noise in a range W2 of thegraph line H in FIG. 5 is estimated to be noise which is attributable toradial fins at opening portions on the outer circumferential side. Inaddition, the noise in a range W1 in which a difference between thegraph lines E and L and the graph lines H and I is large is estimated tobe noise which is generated when an airflow within the flow path isdisturbed by a circumferential rib. Further, the noise in a range W4 ofthe graph line G in FIG. 6 is estimated to be noise which isattributable to the through-holes for bolts. The noise level of thegraph line L for the time when only the through-holes for bolts wereblocked up in the range W4 is 1 to 2 dB lower than the noise level forthe graph line E. Based on this fact, it is considered that the noisewhich is attributable to the through-holes for bolts in the range W4 isof the same level as the noise attributable to airflows that flowthrough a flow path on the disk rear face.

As shown in FIG. 5, the noise level of the brake disc 10 of the firstembodiment which is shown in the range W1 is reduced by a large marginin comparison to the conventional brake disc. The reason is consideredto be that fluctuations in an airflow that passed the circumferentialrib 13 are suppressed significantly by the gradual slope of thecircumferential rib 13. Therefore, it is found that, according to thebrake disc 10 of the first embodiment, noise is reduced by a largemargin without the flow rate of air that releases heat from the brakedisc 10 decreasing significantly.

As shown in FIG. 6, the noise of the brake disc 10A of the secondembodiment which is shown in the range W4 that was generated bythrough-holes is reduced by a large margin in comparison to the graphline G which represents the noise level when only bolt holes were open.It is considered that this is because the annular groove 15 is providedso as to link the plurality of through-holes 12. Thus, it is found that,according to the brake disc 10A of the second embodiment, by reducingthe noise attributable to the through-holes 12, the noise level isreduced by a large margin in comparison to the conventional brake disc.However, it is taken as a premise that noise of the same frequency rangewhich is produced by other factors such as an airflow that flows along aflow path on the rear face of the disc plate portion is reduced.

While a first embodiment and a second embodiment of the presentinvention have been described above, the present invention is notlimited to the foregoing embodiments. For example, the placement of thecircumferential ribs 13 can be changed in various ways, such asproviding the circumferential ribs 13 on the inner circumferentialportion or outer circumferential portion of the disc plate portion, ormidway between the inner circumferential portion and the outercircumferential portion. Further, a structure that narrows a flow pathfor air between pairs of radial fins by means of circumferential ribs isnot limited to a structure in the above embodiments. The circumferentialrib 13 of the foregoing embodiments has a structure that connects a pairof radial fins that are adjacent, and in which the height in therotational axis direction of the disc plate portion is lower than theheight of the radial fin. However, for example, the circumferential ribmay have a structure that has the same height as the radial fin, but inwhich the extent of the circumferential rib in the lateral direction(extent in the circumferential direction of the disc plate portion) doesnot extend over the whole area between the pair of radial fins andleaves a part of the region over which the circumferential rib does notextend. In other words, the circumferential rib may have a structure inwhich there is a flow path for air between the radial fins and thecircumferential rib, or in which there is a flow path for air betweenthe circumferential rib that is connected to a radial fin on one sideand the other radial fin. In this case, the vertex portion of thecircumferential rib corresponds to an end in the rotational axisdirection of the disc plate portion (end facing the flow path for air).In addition, in this case also the circumferential rib may be providedat various positions such as at an inner circumferential portion orouter circumferential portion of the disc plate portion, or midwaybetween the inner circumferential portion and the outer circumferentialportion. Further, although in the embodiments described above astructure is adopted in which the top part of all of the radial finscontacts one side of the wheel, a structure may be adopted in which asmall gap arises between the top part of some of the radial fins and oneside of the wheel. In addition, although in the embodiments describedabove the radial fins are made approximately the same length as thelength in the radial direction of the disc plate portion, the radialfins may have a structure that has a shorter length than the length inthe radial direction of the disc plate portion. Further, the groove 15need not be formed to be along the same diameter of the disc plateportion. Even in such a case, a noise reducing effect is obtained. Inaddition, the details described in the embodiments can be appropriatelychanged within a range that does not depart from the gist of theinvention.

(Third Embodiment)

FIG. 8 is a graph that illustrates the relation between the volume of acircumferential rib and a bolt stress range. Here, the term “bolt stressrange” refers to a fluctuation range from stress that arises in a boltin a state in which a disc does not thermally expand to stress thatarises in a bolt in a state in which a disc thermally expanded. FIG. 9is a chart for describing each of a first form L1 to a fifth form L5 ofa circumferential rib and a comparative form L6 shown in FIG. 8.

Hereunder, a direction along the plate surface of the brake disc 10 isdefined as the horizontal direction, a direction perpendicular to theplate surface is defined as the height direction, and thecircumferential direction of the brake disc 10 is defined as thecircumferential direction of each portion.

The brake disc 10 thermally expands due to frictional heat duringbraking of a railway vehicle, and as a result the tensile stress andbending stress of the bolt changes. The ordinate in FIG. 8 representsthe stress range (difference between highest value and lowest value) oftensile stress and bending stress that arises in a bolt when a certaintemperature change is applied to the brake disc 10. The abscissa in FIG.8 represents the volume of the circumferential rib. The respectivevalues plotted on the graphs in FIG. 8 represent a stress range withrespect to the volume of the circumferential rib when circumferentialribs 13 of the first form L1 to the fifth form L5 in FIG. 9 are adoptedas well as for the comparative form L6 (case without a circumferentialrib).

In the circumferential ribs 13 of the first form L1 to the fifth form L5in FIG. 9, the height is constant, and the length of a top-parthorizontal portion Ld, the shape of a top-part gradual slope SL0 and theshape of a base-part gradual slope SL1 differ as shown in the chart inFIG. 9. The term “top-part horizontal portion Ld” refers to a horizontalregion that is provided at the vertex portion of the circumferential rib13. The term “top-part gradual slope SL0” refers to a sloped portionfrom the vertex portion of the circumferential rib 13 to a base part oran interruption portion. The term “base-part gradual slope SL1” refersto a sloped portion of the base part of the circumferential rib 13. Thecharacter “R” in the chart denotes radius of curvature [mm]. Thetop-part gradual slope SL0 and the base-part gradual slope SL1 aredisposed on the inner circumferential side of the circumferential rib13.

As illustrated in the graph in FIG. 8, the stress range of the boltchanges depending on the volume of the circumferential rib 13 that islocated in the vicinity of the bolt. For example, if the circumferentialrib 13 has a shape as illustrated in the first form L1 in FIG. 9 thathas a large volume, the rigidity of the circumferential rib 13 will belarge and hence the stress range of the bolt will be large. On the otherhand, if the circumferential rib 13 has a shape as illustrated in thefifth form L5 in FIG. 9 that has a small volume, the rigidity of thecircumferential rib 13 will be relatively small, and hence the stressrange of the bolt will also be small. Based on the graph in FIG. 8, bymaking the volume of the circumferential rib 13 less than or equal tothat of the fifth form L5, the stress range of the bolt will be equal tothe stress range in the case of the comparative form L6 in which thereis no circumferential rib 13.

As described above, in a case where the volume of the circumferentialrib 13 is increased to reduce the noise, the problem arises that thestress range of the bolt increases. Therefore, the brake disc of thethird embodiment has a circumferential rib 13A (see FIG. 10) that canreduce noise without large increase in the stress range of a bolt.

FIG. 10 is a view for describing the circumferential rib of the thirdembodiment. FIG. 11 is a frequency graph showing a comparison of thenoise levels between the circumferential ribs of the third embodimentand a conventional circumferential rib. FIG. 12 is a chart showing theforms of the circumferential ribs that are compared in FIG. 11.

The circumferential rib 13A of the third embodiment includes a top-partgradual slope SL0 on the inner circumferential side. The top-partgradual slope SL0 is provided in the range of a section La1 in a radialdirection of the disc plate portion on the inner circumferential side ofthe circumferential rib 13A, and in the range of a section La2 in therotational axis direction of the disc from the vertex of thecircumferential rib 13A. Preferably, the top-part gradual slope SL0 isprovided at least in an area where both of the sections La1 and La2 are2 mm or more, and is a convex curved face having an R of 2 mm or asloping face that is more gradual than such a convex curved face.Further preferably, the top-part gradual slope SL0 is provided at leastin an area where both of the sections La1 and La2 are 5 mm or more, andis a convex curved face having an R of 5 mm or a sloping face that ismore gradual than such a convex curved face.

The circumferential rib 13A of the third embodiment further includes, onthe inner circumferential side, a straight line section Lb that extendsto the top-part gradual slope, and a base-part gradual slope SL1. Itsuffices to make the straight line section Lb near to vertical within amanufacturable range. By this means, the volume of the circumferentialrib 13A can be made small. Further, if a margin exists with respect tothe bolt stress range, the straight line section Lb may be provided withan inclination. Further, the straight line section Lb may be configuredas a curved surface section that has a gradual curvature.

The base-part gradual slope SL1 is, for example, a concave curved facehaving an R of 5 mm. However, the base-part gradual slope SL1 may alsobe a flat surface or a curved surface with a slope that is easy tomanufacture. Further, the base-part gradual slope SL1 may be omitted tothe extent allowed within a manufacturable range.

Further, the circumferential rib 13A of the third embodiment may includea top-part horizontal portion Ld, or need not include a top-parthorizontal portion Ld. In a case where the circumferential rib 13Aincludes a top-part horizontal portion Ld, the range of the top-parthorizontal portion Ld is preferably made around 1 mm to 20 mm. Thelarger the top-part horizontal portion Ld is, the greater the volume ofthe circumferential rib 13A becomes, and the greater the influencethereof on the stress range of a bolt. Therefore, it suffices to set thesize of the top-part horizontal portion Ld to an appropriate size inconsideration of the bolt stress range and the required strength of thecircumferential rib 13A. In addition, the outer circumferential side ofthe circumferential rib 13A may be formed as a vertical structure or maybe provided with a gradual slope within a manufacturable range. As theslope of the outer circumferential side of the circumferential rib 13Abecomes more gradual, the volume of the circumferential rib 13A becomeslarger and the bolt stress range increases. Therefore, it suffices toappropriately set the outer circumferential side of the circumferentialrib 13A within a range such that there is some margin in the bolt stressrange. Further, the height of the circumferential rib 13A can beappropriately adjusted by means of the length of the straight linesection Lb.

<Actions and Effects>

FIG. 11 is a frequency graph that shows a comparison between the noiseof circumferential ribs of the third embodiment and a conventionalcircumferential rib. FIG. 12 is a chart showing the shapes of thecircumferential ribs in FIG. 11. FIG. 13 is a graph in which overallnoise levels in a range from 400 Hz to 5000 Hz are compared.

In this case, a partial model of the area between a pair of adjacentradial fins 11 a and 11 b was created, air was caused to flowtherethrough at a predetermined air velocity, and the noise wasmeasured. The flow path for air between the radial fins 11 a and 11 bwas placed, in a simulated manner, in a state in which the flow path wasenclosed by one side of the disc plate portion and one side of the plateportion of the wheel 100. Further, the circumferential rib 13A wasdisposed so as to block one part of the flow path. The ordinate in FIG.11 represents the noise level of each frequency band, and the abscissain FIG. 11 represents the center frequency of a one-third octave band.Further, “O.A” described on the abscissa represents “overall”, and“P-O.A” described on the abscissa represents overall in a range of 400Hz to 5000 Hz.

In this case, noise was measured for the circumferential ribs 13A fromthe first form P1 to the seventh form P7 in FIG. 12. In the chart inFIG. 12, “R” denotes the radius of curvature [mm], “top-part gradualslope shape” denotes the radius of curvature of the convex curved faceof the top-part gradual slope SL0, and “base-part gradual slope shape”denotes the radius of curvature of the concave curved face of thebase-part gradual slope SL1 in FIG. 10. Further, as a comparison object,a circumferential rib having a current shape that was formed in across-sectionally rectangular shape by cutting was also tested alongwith the circumferential ribs.

As illustrated in FIG. 11, it was confirmed that when thecircumferential ribs 13A of the first form P1 to the seventh form P7were adopted, the noise level could be reduced in comparison to thecircumferential rib with the current shape. Further, when the overallnoise levels in the range of 400 Hz to 5000 Hz were compared, asillustrated in FIG. 13, it was confirmed that, in comparison to thecurrent shape, the noise level can be markedly reduced by adopting thefirst form P1 to the seventh form P7.

Note that, when measuring these respective noises, slight differencesarose in the air quantity (flow velocity) that passed between the pairof radial fins 11 a and 11 b due to differences in the shapes of thecircumferential ribs 13A. In the case of the actual brake disc 10, theair quantity is set to a predetermined value by adjusting the height ofthe circumferential rib 13A so that an appropriate cooling effect isobtained. Further, the flow velocity influences the noise level.Therefore, with regard to the values of the graph in FIG. 13, acorrection was performed so as to remove variations in the noise levelscaused by variations in the flow velocity.

In FIG. 13, based on a comparison of the test results for the third formP3 and the seventh form P7, it is found that the slope of the straightline section Lb does not significantly influence the noise level.Further, based on a comparison of the test results for the first form P1to the third form P3, it was confirmed that the section La2 and shape ofthe top-part gradual slope SL0 influence the noise level.

Further, it was confirmed that when the circumferential rib 13A is thefirst form P1 in which the top-part gradual slope SL0 is made a convexcurved face having the section La1 and section La2 that are each 2 mmand a radius of curvature R of 2 mm, the overall noise level in therange of 400 Hz to 5000 Hz can be reduced by approximately 10 dB (A)relative to the current shape. In addition, when the circumferential rib13A is the second form P2 in which the top-part gradual slope SL0 ismade a convex curved face having the section La1 and section La2 thatare each 5 mm and a radius of curvature R of 5 mm, the overall noiselevel in the range of 400 Hz to 5000 Hz can be reduced by approximately14 dB relative to the current shape. Furthermore, when thecircumferential rib 13A is the fifth form P5 in which the top-partgradual slope SL0 is made a convex curved face having the section La1and section La2 that are each 5 mm and a radius of curvature R of 10 mm,the overall noise level in the range of 400 Hz to 5000 Hz can be reducedby 18.5 dB relative to the current shape.

Based on these test results, it is found that according to thecircumferential rib 13A of the third embodiment, the noise level can bemarkedly reduced.

As described above, according to the brake disc 10 of the thirdembodiment, the level of noise that arises at the location of thecircumferential rib 13A can be markedly reduced without large increasein the bolt stress range.

(Fourth Embodiment)

FIG. 14 is a multiple view drawing for describing forms of a groove thatis provided in a front face of a disc plate portion, in which FIG. 14Ato FIG. 14E show a first form to a fifth form of the groove,respectively. Note that FIG. 14 shows views that were subjected tocoordinate transformation so that the circumferential direction andradial direction of the brake disc 10A become straight line directionswhich are orthogonal to each other in one section of grooves 15A and15B.

In the brake disc 10A of the fourth embodiment, a groove 15A having asmall width is adopted instead of the groove 15 of the secondembodiment. The width of the groove 15A is smaller than the diameter ofan opening portion 12F on a front face side (sliding surface side of thebrake disc 10A) of the disc plate portion of the through-hole 12.Specifically, the diameter of the opening portion 12F is, for example,36 mm, and the width of the groove 15A is, for example, 5 mm, 10 mm, 20mm or the like. In a case where the opening portion 12F is not circular,the width of the groove 15A is smaller than the width of the openingportion 12F in the radial direction of the disc plate portion. The term“width of the groove 15A” means the width of the groove 15A in theradial direction of the disc plate portion.

The sliding-contact member 200 contacts the front face of the brake disc10A to generate a braking force. Therefore, the groove 15A that isprovided in the sliding surface of the brake disc 10A decreases thesliding surface. When the sliding surface decreases, if the pressure ofthe sliding-contact member 200 is the same, it results in an action thatreduces the braking force. Further, when the width or depth of thegroove 15A increases, it results in an action that reduces the strengthof the brake disc 10A.

The groove 15A having a narrow width as described above is adopted forthe brake disc 10A of the fourth embodiment. Therefore, in the fourthembodiment it is possible to secure the area of the sliding surface ofthe brake disc 10A and maintain the strength of the brake disc 10A whilereducing noise that arises at the through-holes for bolts 12 by means ofthe groove 15A.

In a case where the groove 15A having a narrow width is adopted, thereare variations with respect to the form of connection between pairs ofadjacent opening portions 12F and the groove 15A. Examples of suchvariations include a pattern in which the groove 15A connects innercircumferential portions Ri of a pair of adjacent opening portions 12F(FIG. 14A), a pattern in which the groove 15A connects center portionsRc of adjacent opening portions 12F (FIG. 14B), and a pattern in whichthe groove 15A connects outer circumferential portions Ro of adjacentopening portions 12F (FIG. 14C). In addition, there is a pattern inwhich, among a pair of adjacent opening portions 12F, the groove 15Adiagonally connects from the outer circumferential portion Ro of one ofthe opening portions 12F to the inner circumferential portion Ri of theother opening portion 12F (FIG. 14D). In addition, there is a pattern(hereinafter, referred to as “staggered”; FIG. 14E) in which aconnection between the inner circumferential portions Ri and aconnection between the outer circumferential portions Ro of pairs ofadjacent opening portions 12F are alternately repeated and the like. Theterms “inner circumferential portion Ri”, “center portion Rc” and “outercircumferential portion Ro” refer to the respective portions when theopening portion 12F is divided into three portions at equal intervals inthe radial direction of the brake disc 10A.

With respect to the connection patterns of the groove 15A of the fourthembodiment, the connection patterns from FIG. 14B to FIG. 14D areincluded among the aforementioned plurality of patterns, and theconnection patterns of a groove 15B illustrated in FIG. 14A and FIG. 14Eare excluded.

That is, in the fourth embodiment, in a case where the width of thegroove 15A is not more than one half of the diameter of the openingportion 12F, with respect to the connection locations between the groove15A and the opening portions 12F, a connection location excluding theinner circumferential portion Ri of the opening portion 12F is adoptedfor the connection with at least one of the pair of opening portions 12Fand 12F. The term “connection location excluding the innercircumferential portion Ri” means the center portion Rc, the outercircumferential portion Ro, or a portion that straddles the centerportion Rc and the outer circumferential portion Ro of the openingportion 12F. For example, a width of 5 mm or 10 mm or the like isappropriate as the width of the groove 15A.

Further, in the fourth embodiment, in a case where the width of thegroove 15A is greater than one half of the diameter of the openingportion 12F, with respect to the connection locations between the groove15A and the opening portions 12F, a connection location that does notinclude an inner circumference end of the opening portion 12F is adoptedfor the connection with at least one of the pair of opening portions 12Fand 12F. The term “inner circumference end” refers to an end portion ofthe opening portion 12F that is nearest the inner circumference of thebrake disc 10A. A case where the width of the groove 15A is greater thanone half of the diameter of the opening portion 12F is, for example, acase where the groove width is 20 mm. Note that, irrespective of thegroove width and connection locations, the groove 15A preferably has adepth such that the bottom of the groove is located at a height that issubstantially equal to the height of the vertex portion of a bolt or anut.

<Actions and Effects>

FIG. 15 is a graph showing the relation between the frequency of noiseand the noise level for each groove width. FIG. 16 is a graph showingthe relation between the frequency of noise and the noise level for eachconnection location of the groove. FIG. 17 is a graph showing the noiselevel in a frequency range from the 1250 Hz band to the 5000 Hz band foreach connection form of the groove. In these drawings, the forms of theplurality of grooves that are the objects are described in the format“connection location—groove width”. In the form “center portion—20 mm”,although the groove 15A is connected to a part of the outercircumferential portion Ro and also a part of the inner circumferentialportion Ri of the opening portion 12F since the groove 15A is one halfor more of the diameter of the opening portion 12F, the form is shown asone in which the center of the groove 15A is connected so as to overlapwith the center of the center portion Rc. The ordinate in FIG. 15 andFIG. 16 represents the noise level for each one-third octave band, andthe abscissa in FIG. 15 and FIG. 16 represents the center frequency foreach one-third octave band. The ordinate in FIG. 17 represents the noiselevel in the frequency range from 1250 Hz to 5000 Hz.

Among the forms that are the objects, the patterns “center—5 mm”,“center—10 mm”, “center—20 mm”, “outer circumference—10 mm” and“diagonal—10 mm” are examples of forms that are adopted in the fourthembodiment. The patterns “no groove”, “inner circumference—10 mm” and“staggered—10 mm” are examples of comparative forms that are not adoptedin the fourth embodiment.

Based on the results shown in FIG. 15, it is found that when the widthof the groove 15A is narrowed, the noise reduction effect graduallydecreases. On the other hand, based on the results in FIG. 15, it isfound that in comparison to the case where there is no groove, a noisereduction effect is obtained even when there is a groove with a width ofonly 5 mm. Further, based on the results in FIG. 16 it is found that, ina case where the width of the groove 15A is narrow, the noise reductioneffect varies depending on the connection location with respect to thepair of adjacent opening portions 12F.

Further, based on the results in FIG. 17 it is found that, althoughnoise is reduced by the pattern “inner circumference—10 mm” and thepattern “staggered—10 mm”, the effect is small, while in contrast, anoticeable noise reduction effect is obtained by the patterns adopted inthe fourth embodiment. Based on these results it is found that, byadopting the aforementioned connection forms between the groove 15A andthe opening portions 12F, noise that is generated at the location of thegroove 15A can be markedly reduced.

As described above, according to the brake disc 10A of the fourthembodiment, noise that arises due to the through-holes for a bolt 12 canbe markedly reduced without significantly reducing the sliding area.

INDUSTRIAL APPLICABILITY

The present invention can be utilized in a brake disc for a railwayvehicle.

REFERENCE SIGNS LIST

-   10, 10A Brake Disc-   10 f Front Face (Sliding Portion)-   10 r Rear Face-   11 a, 11 b Radial fin-   12 Through-hole-   12F Opening Portion-   13, 13A Circumferential rib-   13 a Side Face on Inner Circumferential Side-   13 b Side Face on Outer Circumferential Side-   15, 15A, 15B Groove-   La1, La2 Section of Top-part Gradual Slope-   Lb Straight Line Section-   Ri Inner Circumferential Portion-   Rc Center Portion-   Ro Outer Circumferential Portion-   SL0 Top-part Gradual Slope-   SL1 Base-part Gradual Slope

1. A brake disc for a railway vehicle, comprising: a disc plate portion having a sliding portion on a front face, a plurality of radial fins provided on a rear face of the disc plate portion and having a shape extending in a radial direction of the disc plate portion, and a circumferential rib provided between each pair of radial fins that are adjacent among the plurality of radial fins, and having a shape extending in a circumferential direction of the disc plate portion, wherein: a flow path for air that runs from an inner circumferential side to an outer circumferential side of the disc plate portion is formed between the pair of radial fins in a state in which the disc plate portion is fastened to a wheel of a railway vehicle, and the flow path for air is narrowed by the circumferential rib; and a gradual slope for suppressing fluctuations in an airflow that passes between the pair of radial fins is provided on the circumferential rib on a side face along the radial direction of the disc plate portion.
 2. The brake disc for a railway vehicle according to claim 1, wherein the gradual slope is provided on one side face of the circumferential rib that faces the inner circumferential side along the radial direction of the disc plate portion, or is provided on both side faces of the circumferential rib that face the inner circumferential side and the outer circumferential side, respectively, along the radial direction of the disc plate portion.
 3. The brake disc for a railway vehicle according to claim 1, wherein: the gradual slope includes a top-part gradual slope that is provided at least at a top part of the circumferential rib, and the top-part gradual slope is a convex curved face having a radius of curvature of 2 mm or is a sloping face which is more gradual than the convex curved face, the top-part gradual slope being provided at a side portion facing the inner circumferential side of the disc plate portion, at a section of 2 mm or more in the radial direction of the disc plate portion, and at a section of 2 mm or more in a rotational axis direction of the disc plate portion from a vertex of the circumferential rib.
 4. The brake disc for a railway vehicle according to claim 1, wherein: the gradual slope includes a top-part gradual slope that is provided at least at a top part of the circumferential rib, and the top-part gradual slope is a convex curved face having a radius of curvature of 5 mm or a sloping face which is more gradual than the convex curved face, the top-part gradual slope being provided at a side portion facing the inner circumferential side of the disc plate portion, at a section of 5 mm or more in the radial direction of the disc plate portion, and at a section of 5 mm or more in a rotational axis direction of the disc plate portion from a vertex of the circumferential rib.
 5. The brake disc for a railway vehicle according to claim 1, wherein the circumferential rib connects the pair of radial fins, and having a flow path for air between the wheel and the circumferential rib. 